The invention relates to a fuel supply system for mixture compressing, externally ignited internal combustion engines which have an induction manifold and, disposed in series therein, an air-flow measuring member or sensor and an arbitrarily settable butterfly valve. The air-flow measuring member is displaced in proportion to the air flow against a restoring force and this displacement moves the movable part of a fuel quantity metering and distribution valve assembly disposed in the fuel line for the purpose of metering out a fuel quantity in proportion to the air quantity. The restoring force acting on the air-flow measuring member is produced by pressurized fluid delivered through a pressure line and this fluid impinges continuously and at constant, but arbitrarily changeable, pressure on a control slide which transmits the restoring force to the air-flow sensor. The pressure of the fluid may be changed by at least one pressure control valve subject to engine parameters. The pressure control valve contains a temperature-dependent, heatable control element embodied as a bi-metallic spring. The bi-metallic spring is thermally insulated with respect to its environment and is directly connected to a heat-conducting bracket which is electrically heated as soon as the engine is started. As long as the engine temperature is below the normal operating temperature, the bi-metallic spring opposes a control spring located within the pressure control valve.
It is the purpose of fuel injection systems of this type to establish favorable fuel-air mixtures automatically for all operational states of the internal combustion engine so as to cause as complete a combustion of the fuel as possible and to prevent, or at least to sharply reduce, the generation of toxic components in the exhaust gas while maintaining the highest possible performance of the lowest possible fuel consumption of the internal combustion engine. Achieving this goal requires very precise fuel metering adapted to the requirements of each operational state of the engine. Thus, for example, it must be possible to change the average fuel-air ratio in dependence on engine parameters, for example, on the engine temperature and the exhaust-gas composition.
In known fuel supply systems of this type, the fuel quantity is metered out as nearly proportional as possible to the air quantity flowing through the induction tube and the ratio of the metered-out fuel quantity to the air quantity can be altered by changing the restoring force acting on the air-flow measuring member in dependence on engine parameters. Separate pressure control valves govern the warm-up phase and the regulation of the air number, which is defined to be proportional to the air-fuel ratio and assumes the value .lambda. = 1.0 stoichiometric air-fuel mixture.